The present invention relates to semiconductor structures, and particularly to a back-end-of-line (BEOL) resistive structure comprising a doped semiconductor material, and design structures for the same.
Doped semiconductor materials are employed to form high resistivity elements in semiconductor devices such as a resistor or an electrical fuse. A resistor is a resistive circuit element that maintains a constant resistance value, and may be used in an RC circuit or any other circuit that requires an element with a constant resistance. An electrical fuse is a resistive circuit element that may change the value of the resistance upon programming. For example, when high electrical current flows through an electrical fuse, the material of the electrical fuse may be electromigrated or ruptured, thereby raising the resistance of the electrical fuse typically at least by an order of magnitude.
In the prior art, resistors and electrical fuses employing a doped semiconductor material are typically formed within a semiconductor substrate, i.e., below a top surface of a single crystalline semiconductor substrate, or at a gate level, i.e., at the same level as gate conductor lines. In the case of resistors and electrical fuses formed in the semiconductor substrate, dopants are introduced into portions of the semiconductor substrate to lower the resistivity of the semiconductor substrate sufficiently so that the doped semiconductor material has a reduced level of resistivity. In the case of resistors and electrical fuses formed at gate level, a doped polycrystalline semiconductor layer is formed directly on a gate dielectric layer by deposition of a doped semiconductor material or by deposition of an undoped semiconductor material. The doped semiconductor layer is lithographically patterned to form resistors and electrical fuses.
The doped semiconductor material has a higher resistivity than metallic materials, typically by at least two orders of magnitude. In the case of doped silicon, resistors and electrical fuses having a resistivity in the range from about 1.0×10−4 Ohm-cm to about 1.0 Ohm-cm may be formed by employing in-situ doping and/or ion implantation.
Such prior art doped semiconductor material form resistive structures located in the semiconductor substrate or directly on a gate dielectric below the first line level metal wiring structures, i.e., the level of metal lines that are closest to the semiconductor substrate. For this reason, the prior art resistive structures formed in the substrate or directly on a gate dielectric are “front-end-of-line” (FEOL) semiconductor structures located below the level of the first line level metal wiring structures and formed prior to formation of the first line level metal wiring structures. Each such FEOL resistive structure occupies an area of a semiconductor substrate that no other FEOL semiconductor device may occupy. Thus, formation of a FEOL resistive structure according to the prior art reduces area for other semiconductor devices, thereby limiting device density for FEOL semiconductor devices.
Further, the height or depth of the prior art FEOL resistive devices is limited either by the thickness of the gate conductor layer and the energy distribution of ion implantation. In addition, the width of the prior art FEOL resistive devices are limited by lithographic constraints since lithographic patterning determines the width of the prior art FEOL resistive devices. Thus, formation of a relatively high resistance structure requires a large structure located in or directly on the semiconductor substrate.
In view of the above, there exists a need for a resistive structure that occupies as small space as possible in front-end-of-line (FEOL) device areas, i.e., the volume beneath a first level metal wiring structures, and design structures for the same.
Further, there exists a need for a resistive structure that may provide a high resistance value with a minimal device volume, and particularly a resistive structure that may have a sublithographic width, and design structures for the same.